1. Field of the Invention
The present invention relates to a developing unit having a preheating apparatus, and more particularly, to an improved developing unit having a preheating apparatus capable of ensuring good quality of printing by providing a preheating apparatus inside of a developing unit which stores a toner and maintains the toner at a predetermined temperature and humidity.
2. Description of the Related Art
In an earlier electrophotographic image forming device which is used in a duplicating apparatus and in a laser printer, when the surface of an organic photoconductive drum (OPC) is evenly charged by a corona discharge of a charging unit, an electrostatic latent image is formed on the charged surface of the OPC drum by exposure. The electrostatic latent image is changed into a visible image after it is developed by a toner when it passes a developing unit, and the visible image is transferred onto a paper by a transfer unit.
A transferred visible image is fixed on the paper by the heat and pressure of a thermal roller and a press roller when the paper passes the fixing unit. Small amounts of toner and the electrostatic latent image remain on the surface of the OPC drum, passing the transfer unit. The toner is removed by a cleaner, and the latent image is removed by a latent image removing lamp.
First, developing is performed when the toner sticks to the electrostatic latent image formed on the surface of the OPC drum. That is, in the case of a printer using an electrophotographic image forming method, as light from a laser beam or a light emitting diode LED is modulated according to the printing data received by the printer from a computer and the OPC drum is exposed, the electrostatic latent image, i.e., an electrical image similar to an image to be printed is formed on the surface of the OPC drum. At this time, the toner inside of the developing unit selectively sticks to the electrostatic latent image formed on the surface of the OPC drum by the operation of the electrical and physical power.
When the developing is completed through the above-described process, the toner on the surface of the OPC drum is transferred onto the paper by the electrical operation and the toner is fused to the paper by heat and pressure. The toner used in the electrophotographic image forming device is dependent upon the temperature and humidity of the circumferential factors. For example, after the electrophotographic image forming device is not used for a long time and is left at a low temperature and low humidity, when the device is used again, as the developing characteristic of the toner have already changed due to the circumferential factors of low temperature and low humidity, these factors may result in a printed image of poor quality.
U.S. Pat. No. 4,027,621, to Kane et al., entitled Developing System For electrostatic Reproduction Machines, discloses a developing apparatus for electrostatic copier having a heating means to heat the toner so as to have a proper temperature and humidity.
The defensive publication of Kasper et al., Defensive Publication No. T956,001, entitled Electrographic Apparatus And Process For Humidity Stabilized Development, discloses an electrophotographic apparatus including a heat generating to heat the toner so as to maintain its proper humidity. The patent to Denton et al., U.S. Pat. No. 5,574,547, entitled Liquid Electrophotographic Reproduction Machine Employing Heated Carrier Liquid, discloses a liquid electrophotographic apparatus in which the liquid toner is preheated to a desired temperature.
The following patents each disclose features in common with the present invention but are not as pertinent as the patents discussed in detail above: U.S. Pat. No. 5,247,334 to Miyakawa et al., entitled Image Formation Method And Apparatus With Preheating And Pressure Image Transfer With Liquid Toner Development, U.S. Pat. No. 5,066,988 to Miyake, entitled Electrophotographic Apparatus Having Means For Avoiding Blurring Effects Caused By Idle Intervals, and U.S. Pat. No. 5,436,104 to Yasuda et al., entitled Method Of Forming Fixed Images Using Heated Belt.
While each of the above-noted patents have features in common with the present invention, none of them teaches or suggests the specifically recited combination of elements of the present invention.